The principal objective in the present renewal is to explore and evaluate immunity in schistosomiasis haematobia. The well tested capuchin monkey (Cebus apella) -- Schistosoma haematobium and hamster (Mesocricetus auratus)--S. haematobium systems will be used as study models. Priority will be given to homologous immunity in the first period, followed by investigations in heterologous immunity in which the relatively nonpathogenic microtine, Schistosomatium douthitti, and/or other species, will serve as the immunizing agents for challenge by S. haematobium, S. intercalatum, and other mammalian schistosomes. This would be a step toward possible immunotherapy or immunoprophylaxis. Immunity will be judged by definitive host parasite relationships including: (1) parasite returns and distribution, (2) distribution and intensity of tissue egg deposits, (3) conditions of parasites in different host organs, (4) intrauterine egg counts, and (5) pathology. Pathology in capuchin monkeys exposed to different regimens of infection than in previous studies will be followed closely to determine whether homologous and heterologous challenges influence evolution of pathogenesis in the urogenital system or enhance bladder carcinogenesis. Tissues will be examined for viruses. Urine cytology, X-ray, and examination by laparotomy plus tissue sampling at cystotomy will be employed as parameters for following infections in primates. S. haematobium derived from human infectins and passaged only through primates will be studied to determine whether such lines offer stronger parasites for basic studies in schistosomiasis haematobia. Adult schistosomes will be further characterized by scanning electron microscopy.